1. Field of the Invention
The invention relates to a compressed-air supply unit, a check valve and to a method for operating a compressed-air supply unit.
2. Description of Related Art
A compressed-air supply unit, which is used for example in a dental-medical workplace for providing compressed air, has a pressure accumulator which is filled with the aid of a compressor. When compressed air is withdrawn from the pressure accumulator, the pressure of the air contained in the pressure accumulator falls, so that when the pressure falls below a presettable minimum pressure a manometric switch connected to the pressure accumulator starts the compressor, in order to fill the pressure accumulator again.
Between the pressure accumulator and the compressor, there is provided a check valve, which when the compressor is switched off prevents the compressed air from escaping from the pressure accumulator in the direction opposite the conveying direction of the compressor.
Check valves known hitherto comprise, for this purpose, closing parts which are pressed against a valve seat with the aid of a spring. As soon as the pressure applied to the closing part on the inlet side exceeds the spring force, the check valve opens and the air can be conveyed by the compressor to the pressure accumulator.
A construction of this type constitutes a spring-mass system exhibiting a natural oscillation behaviour which can be excited to oscillate by pressure fluctuations in the air flow. In particular, piston compressors frequently generate an air flow which pulsates with greater or lesser intensity with the rotational frequency of the drive motor, so that the closing part of the check valve during the operation of the compressor hammers on the valve seat with greater or lesser intensity depending on the pressure applied, which may result in disturbing noise generation. This is undesirable in particular when using the compressed-air supply unit in a patient environment as in the case of a dental-medical workplace.